1978 Olds - change the ATF or leave it?

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Jul 17, 2005
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Cleveland, OH
Hey all.

A few years ago, I inherited my uncle's 1978 Oldsmobile Delta 88 Royale with 5.7L gas engine and TH-350 three speed auto.

It had sat in a dry garage for about 20 years. Maybe started a couple times at most.

The first time I drove it, I was very gentle with throttle. The test drive was only a mile or two. It had a tiny bit of slip accelerating from a full stop SOME of the time.

Week later, took it out again on a short drive, only showed slip from a stop once. Next time I drove it - no slips.

This was 4 years ago now, and since then, I've put about 4,000-5,000 miles on it. It hasn't slipped in 4 years. It hasn't done ANYTHING "wrong" in those 4 years. It downshifts when I put my foot down, upshifts as I ease the throttle, shifts are solid and yet smooth. It's a pleasure to drive on sunny weekends.

Car currently has 112,000 original miles. I only drive this car maybe 1,000-2,000 per year. I can't know for certain if the ATF has ever been changed.

1. Should I leave well enough alone, and enjoy it as is?
or
2. If you think I should drop the pan, change the filter and fluid, what fluid would be best? I would hate to mess up the shift quality because the clutches or valves don't like the new fluid.

Brian
 

BlueOvalFitter

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Hey all.

A few years ago, I inherited my uncle's 1978 Oldsmobile Delta 88 Royale with 5.7L gas engine and TH-350 three speed auto.

It had sat in a dry garage for about 20 years. Maybe started a couple times at most.

The first time I drove it, I was very gentle with throttle. The test drive was only a mile or two. It had a tiny bit of slip accelerating from a full stop SOME of the time.

Week later, took it out again on a short drive, only showed slip from a stop once. Next time I drove it - no slips.

This was 4 years ago now, and since then, I've put about 4,000-5,000 miles on it. It hasn't slipped in 4 years. It hasn't done ANYTHING "wrong" in those 4 years. It downshifts when I put my foot down, upshifts as I ease the throttle, shifts are solid and yet smooth. It's a pleasure to drive on sunny weekends.

Car currently has 112,000 original miles. I only drive this car maybe 1,000-2,000 per year. I can't know for certain if the ATF has ever been changed.

1. Should I leave well enough alone, and enjoy it as is?
or
2. If you think I should drop the pan, change the filter and fluid, what fluid would be best? I would hate to mess up the shift quality because the clutches or valves don't like the new fluid.

Brian
 

bxd20

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Cleveland, OH

Nothing personal of course. But that article was total garbage. Most of it was nonsensical rambling, and even when they got to a specific point, it often was wrong. Just one gem: "Don’t worry about overfilling. Especially if you are driving a TH400, it is acceptable to overfill the transmission pan by a quart or an extra ½ percent."

Overfilling IS something to be concerned about.

But even if you want to argue that a slight overfill is OK.... "a quart" versus "an extra 1/2 percent" are in no way similar amounts! A quart is 32 ounces. In a typical trans, an extra 1/2 percent is somewhere around 1 or 2 ounces. Drastically different.
 

BlueOvalFitter

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Nothing personal of course. But that article was total garbage. Most of it was nonsensical rambling, and even when they got to a specific point, it often was wrong. Just one gem: "Don’t worry about overfilling. Especially if you are driving a TH400, it is acceptable to overfill the transmission pan by a quart or an extra ½ percent."

Overfilling IS something to be concerned about.

But even if you want to argue that a slight overfill is OK.... "a quart" versus "an extra 1/2 percent" are in no way similar amounts! A quart is 32 ounces. In a typical trans, an extra 1/2 percent is somewhere around 1 or 2 ounces. Drastically different.
Sorry, I didn't read the whole article. I was just going by the title.
 

bxd20

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Leaning towards using the Castrol Transmax Dex/Merc formula that says "for older model Ford and GM vehicles" on the bottle. I like that it specifically says not to use in GM vehicles designed for Dexron VI. And of course an ACDelco filter.
 
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This sounds like it was written by Kamala Harris' speech writer....

Since synthetic transmission fluids are human-made, they come with a lot of specifications to meet the different transmission needs. Nowadays, automatic engines are coming out more complicated, which requires more protection.
 
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Leaning towards using the Castrol Transmax Dex/Merc formula that says "for older model Ford and GM vehicles" on the bottle. I like that it specifically says not to use in GM vehicles designed for Dexron VI. And of course an ACDelco filter.
Older model Fords use type F fluid while GM used Dexron in it's various formulas. Two different specs. I wouldn't use a fluid that says it's compatible with both when Dexron 6 is backward compatible and relatively cheap.
 
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Older model Fords use type F fluid while GM used Dexron in it's various formulas. Two different specs. I wouldn't use a fluid that says it's compatible with both when Dexron 6 is backward compatible and relatively cheap.
I guess it depends on your definition of what counts as "older model," as Type F hasn't been used in new Ford transmissions for like 40 years, Cars that are now over 30 years old called for Mercon, although almost 20 years ago Ford stated Mercon V should be used on older transmissions calling for Mercon, so I guess technically generic Dex/Merc isn't exactly the right fluid, but I'm not sure if that recommendation was made because Mercon V performs better or because it works well enough and Ford just wanted to consolidate down to fewer fluids like when Chrysler started using ATF+4 in older Jeeps that originally called for Dex II.
 
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I guess it depends on your definition of what counts as "older model," as Type F hasn't been used in new Ford transmissions for like 40 years, Cars that are now over 30 years old called for Mercon, although almost 20 years ago Ford stated Mercon V should be used on older transmissions calling for Mercon, so I guess technically generic Dex/Merc isn't exactly the right fluid, but I'm not sure if that recommendation was made because Mercon V performs better or because it works well enough and Ford just wanted to consolidate down to fewer fluids like when Chrysler started using ATF+4 in older Jeeps that originally called for Dex II.

20 years ago, there were fluids from reputable companies such as Valvoline that met the Mercon, Mercon V, AND Dex III specs. This was before Ford recommended Mercon V for Mercon apps.

And ATF+4 works well as a replacement for Mercon/Mercon V, been running it in my 2004 Ford Crown Vic for several years now...
 

bxd20

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Wish someone still made a pure Dex III spec fluid.

Now it’s a guess to us on what’s closer to Dex III.

The Dex III/Merc combo fluid, OR, Dex VI.
 
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Off the Shelf DEX/MERC is the closest you can get to Dexron III, most likely it's the same fluid they sold before GM pulled all the licenses. If you want a very high quality replacement for Dexron III, use Allison TES-295 fluid, it was essentially and extension of the Dexron III specification for extended drains and better cold performance than standard Dexron III, use whatever brand, they should all be pretty similar BP Autran 295, Mobil Delvac 1 ATF, Allison Transynd 295/468 , Shell Spirax S6 295..
 
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Nothing wrong with changing the fluid now. Maxlife is great stuff. Any synthetic ATF will be a great choice for your car.

If your transmission has a drain plug, great (too bad they stopped including one, though. That was stupid for them to do)
If not, don't worry! There are many aftermarket pans with a drain plug for the TH350 :)

Officially, Dexron VI can be used in all GM transmissions calling for earlier Dexron.
 
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